NSFS | NC | fix bucket policy issue

[romayalon]

Explain the changes

1. bucketspace_fs.read_bucket_sdk_info() added iteration on existing bucket policies in order to convert plain principals (email/"*") string to sensitive strings.
2. bucketspace_fs.put_bucket_policy() - added validate_s3_policy() call.
3. moved validate_s3_policy() func from bucket_server to bucket_policy_utils so it can be re-used by bucketspace_fs.
   since we don't have a system store in NC env, we currently won't check existence of accounts mentioned in bucket policies (see Gaps).
4. Added unit tests

Issues: Fixed #xxx / Gap #xxx

1. Currently we won't check for existence of the accounts provided in the bucket policy as it requires a new account_by_email cache or a different solution.
2. Fixed principal.unwrap is not a function #7527

Testing Instructions:

• Doc added/updated
• Tests added

[naveenpaul1]

a small comment, LGTM